Investigations in hematology will be pursued along the following lines: Copper, iron and porphyrin metabolism - A. Current studies have defined a role for ceruloplasmin in the movement of iron from reticuloendothelial and hepatic parenchymal cells to transferrin. The role of the copper protein, erythrocuprein, in the intracellular metabolism of iron will now be investigated. B. The movement of iron into, through and out of in vitro cultured macrophages will be investigated. C. The role of iron in the pathogenesis of Porphyria Cutanea Tarda is being investigated. Studies on leukocytes - A. Previous studies have described neutrophil kinetics in the blood and bone marrow of normal man and in several disease states. These will be continued. B. Investigations of control mechanisms regulating granulocytopoiesis have demonstrated the existence of a humoral factor which releases marrow neutrophils. Current efforts are directed to development of an assay for "neutropoietic" activity. Hemostasis - A highly purified human factor VIII is being used to study the structure, function and metabolism of this essential coagulation factor.